We have established systems for the clonal analysis of thyroid antigen reactive human T cells. These cells are pivotal in the pathophysiology of autoimmune thyroid disease and our studies have demonstrated for the first time the detailed characteristics of T cells recognizing thyroid cell surface antigens in the context of HLA. This competitive renewal seeks funding to pursue studies intended to define the clonal heterogeneity of the T cell response to defined human thyroid antigen. We shall utilize our previous experience in T cell cloning for the following specific aims: 1. To perform more detailed phenotypic and functional analyses of thyroid antigen specific human T cells using recently- available monoclonal antibodies to phenotypic markers and characterize their lymphokine secretions in relationship to surface phenotype. 2. We will be continuing a project recently initiated in our laboratory evaluating TT cell hybridoma production in order to immortalize thyroid antigen specific T cells. In addition, we will be utilizing retroviruses carrying immortalization genes to infect T cell clones, again in an effort to immortalize the cells. 3. We will determine the human T cell receptor diversity in thyroid-specific T cell clones by examining their interaction with different epitopes of, for example, thyroglobulin. We will also examine their C beta chain usage and use polymerase chain reactions to initiate studies on V beta family usage in the same T cell clones. These experiments will lead to our ability to sequence individual thyroid-specific T cell receptor genes, allowing many new avenues of investigation to determine the etiology of autoimmune thyroid disease. Furthermore, if we find a diverse helper T cell response, as evidenced by a heterogeneous T cell receptor repertoire, this observation will nullify the hypothesis that a single thyroid-specific T suppressor cell defect is important in the etiology of the human autoimmune thyroid diseases.